Blended transformer oil



United States Patent 3,000,807 BLENDED TRANSFORMER OIL Jones I. Wasson, Union, and James E. Kehoe, Clark, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Dec. 4, 1958, Ser. No. 778,085 6 Claims. (Cl. 208-14) This invention is concerned with an improved transformer oil comprising a blend of two select base stocks. More particularly it is concerned with a transformer oil consisting essentially of a blend of an acid treated distillate and a hydrofined distillate which blend surprisingly has a higher uninhibited Doble Oxidation Test life than either of its components.

A major factor in the market acceptance of a transformer oil is good oxidation resistance without the use of added inhibitors. Users of transformer oils have traditionally used uninhibited oils and are suspicious of oils containing inhibitors unless it is known that the base oil itself has good oxidation resistance. This feeling is firm- 1y entrenched. It is due partly to a belief that an inhibitor can be destroyed in the oil or volatilized by severe heat or extreme overloads, and partly to a fear that the oils made by inhibiting the poor base stock give insufficient warning of a coming breakdown. Thus, while it is not clear how the oxidation resistance of an uninhibited transformer oil relates to its performance in use with an inhibitor, it is clear that in order to have a saleable and marketable product, the base oils used in the transformer oil must show excellent uninhibited oxidation resistance. This oxidation resistance is customarily tested by the .conventional Doble Oxidation Test for electrical insulating oils developed by the Doble Engineering Company of Belmont, Massachusetts.

In the Doble oxidation test an oil heated to 95 C. is blown with air in the presence of coils of copper and iron wire which serve as catalysts. At periodicintervals portions of the oil are withdrawn and examined for neutral.- ization number, sediment formation (after 5:1 naphtha dilution) and interfacial tension. The time required for the formation of visible sludge, for the neutralization number to increase to 0.2 mg. per gram, and for the interfacial tension to decrease below 15 dynes per centimeter is reported. A satisfactory oil must have -a life of at least 48 hours before reaching any of these three conditions. e 1

This invention is based upon the very interesting finding that a transformer oil made from a mixture of an acid or oleum-treated naphthenic distillate and a hydrofined naphthenic distillate displays superior uninhibited oxidation resistance. Such a blend of oil has an oxidation life materially better than that ,of either-component. This good oxidation resistance is maintained when the conventional 0.3 wt. percent of an oxidation inhibitorsuch as 2,6-ditertiary butyl 4-methylphenol1 is added. With this amount of oxidation inhibitor in the transformer oil blend of this invention, the transformer oil has a Doble oxidation life exceeding 1000 hours and satisfactorily passes the customarily accepted industrial inspections.

Both the acid treated and the hydrofined. distillates used in the transformer oil blend of this invention must be derived from naphthenic crudes. Suitable Texaslowcold test (naphthenic) crudes are Webster, Thompson, Sugarland, and Amelia, and can be characterized by the following inspections: Gravity API .25/29, sulfur 0.2/0.3, vis. SSU at 100 F. 50/ 80. The distillates can be obtained by conventional atmospheric distillation. Both distillates should have a boiling point in the range of 450 to 900 F. and preferably in the range of 460 to -775 R, an API gravity in the range of to and ice preferably in the range of 27 to 28, a viscosity F. in the range of 55 to SSU. 1

The hydrofined component is prepared in a conventional manner by contacting the naphthenic distillate with a hydrofining catalyst in the presence of hydrogen. The temperature of operation is important. Too high a temperature seems to remove too manyof the natural inhibitors, and too low a temperature does not sufficiently correct the instability of the oil. Most advantageously, the temperature used is in the range of 550 to 650 F. During hydrofining, the feed rate is important. Best results are obtained when the feed rate is in the range of 1 to 3 volumes of feed per volume of catalyst per hour (v./v./hour). 500 to 900 standard cubic feet (s.c.f.) per barrel of free hydrogen are used in the hydrofining zone during treatment of the oil. Pressure is not critical and can be of the order of 500 to750 p.'s.i.g. Any suit,- able hydrofining catalyst can be used such as cobalt molybdate on alumina, and'the like. It is preferredto use a 0601P/0301P type catalyst known commercially as Harshaw 0301P and Harshaw 06011 'sold by the Harshaw Chemical Company. This hydrofining operation is well known and involves passing the oilat the indicated feed rate and temperature over a fixed bed of the-catalyst, while diluted with the indicated amount of hydrogen.

The acid-treated distillate is prepared by the well established sulfuric acid treating process and usually' a batch or semi-continuous operation is carried out with one or two dumps. The acid sludge resulting from the treatment is settled and withdrawn after each dump and prior to the 'addition of a subsequent dump of acid. Preferred acid-treated distillates are prepared according to this invention when 0.5 to 1.0 lb. per gallon of sulfuric acid in a concentration in the range of 96 to 105% is used at a temperature in the range of to 105 F. and the oil is recovered in yields in the range of 97 to 98 volume percent; The acid-treated distillate should have a 1 to +18 Saybolt color.

It is known to those skilled in the art that the acid treatment of an oil is usually followed by neutralization, as with sodium bicarbonate, followed by steaming at a temperature of 225 to 250 F. and clay contacting or percolation. Both the hydrofined distillate and the acid treated distillate must be treated or contacted with clay in order to arrive at an acceptable product. Clay C011". tacting or percolating is a well established petroleum oil process and involves decolorizing of the oilsbycontact with finely divided clays such as'fullers earth or bleaching clays. The clays remove soaps from petroleum fractions and increase the oxidation stability. Suitable industrial clays useful in this invention are Bennett-Clark natural clay and Attapulgus, For reasons not quite clear I yet, it appears that clay percolation gives better results than clay contacting. Preferably, 0.6 to l pound/gal of absorbent clay is contacted with the distillate, oil ati a temperature in the range of 250 to 300 F. Clay perf colation is carried out at temperatures in the range of 80 tol05F.

The hydrofined and clay-treated distillate preferably has a boiling point in the range of 460 fto 775 F., and API gravity in the range of 27 to 30, and a viscosity at 100 F. in the range of 55 to'60. The acid and claytreated distillate preferably has a boiling point" in tli range of 460 to 775 F., an API gravity inthe range of 27 to 30, and a viscosity at 100 F. in vthe range of 55 to 60 SSU. f- The two distillate oils are blended according to this invention in proportions of 50 to 80 vol. percent of the hydrofined distillate, and 50 to 20 -vol percent of the acid-treated oil. The use of a greater meant of the acid-treated oil is undesirable because it would "lead to some loss in oxidation stability anditwould bernore EXAMPLES The acid-treated oil used to form the following blends was obtained by treating a 460 to 775 F. distillate obtained from a coastal crude with 2 /2 vol. percent oleum at 190 F. and recovering the treated oil after one dump in a yield of 97.6%. This acid-treated oil was then neutralized with a 15% sodium bicarbonate solution, followed by two isopropyl alcohol and water washes. The neutralized oil was then steamed at 225 F. using about 0.5 lb. of steam per lb. of oil. The steamed oil was then percolated through 0.6 lb. per gallon of an Attapulgus type clay at 80-105 F. to arrive at the final product. The final acid-treated oil had a boiling point in the range of 460 to 775 R, an API gravity of 28.1 and a viscosity at 100 F. of 58 SSU.

The hydrofined distillate oil used in these blends was obtained by hydrofining a distillate boiling in the range of 460 to 775 F. obtained from a coastal crude. The hydrofining was carried out over a cobalt molybdate type catalyst sold commercially as Harshaw 0301P or 0601P by the Harshaw Chemical Company. The temperature of hydrofining was 625 F. and the pressure was 750 p.s.i. The feed rate was 1.1 v./v./hr. and the hydrogen rate was 900 s.c.f./bbl. The distillate oil so hydrofined was then treated with a natural type clay sold by the Bennett-Clark Company. 0.8 lb, of clay per gallon of oil was used. The oil was percolated through the clay at a temperature of 300 F. The finished oil had a boiling point in the range of 460 to 775 F., an API gravity of 285, and a viscosity at 100 F. of 56.8 SSU.

These two oils were blended in the proportions indicated in the following tables.

Table l [Blends (wt. percent)] Hydrofined 50 70 80 100 Acid Treated 1 100 50 30 20 0 Doble Oxidation Test:

Uninhibited-Hours:

To 0.2 Neut. N0 140 192+ 240 200 40 To 15 IFT 140 192+ 200 150 40 T0 Sludge 72 72 72 72 40 Inhibited (0.31, 2,6 (11- tertiary Butyl 4-Methy1 Phenol):

Doble Life, Hours 1, 280 l, 780 l, 200 1, 500

1 Oleum treated.

Table II [Blends (wt. percent)] Hydroflned 0 70 50 100 Acid Treated 1 100 30 50 0 Doble Oxidation Test:

Uninhibited-Hours:

To 0.2 Neut. N0 140 200 200 40 To 15 IFT 140 200 200 40 To Sludge 48 48 40 Inhibited (0.31, 26 di-te Butyl 4-Methyl Phenol):

Doble Life, Hours 1, 100 1, 280 1, 500

l 98% Sulfuric acid treated.

Table III EFFECT OF HYDROFINING TEMPERATURE ON DOBLE OXIDATION STABILITY Catalyst: Cobalt molybdate on alumina 750 p.s.i.g., 2.0 v./v./hr.

450 s.c.f./bbl. Hz

1.0 lbJgal. Bennett-Clark clay 300 F.

'Iemp., F 475 575 625 675 Sample N o 1 2 3 1 4 Hrs. to 0.2 N eut. No 240 120 2 72 3 48 Hrs. to Sludge 48 72 72 48 Hrs. to 15 IFI 240+ 120+ 72 48 1 0.7 lbs/gal. clay. Neut. No. 0.31 at 72 hours. 3 Neut. No. 0.81 at 48 hours.

Table IV EFFECT OF FEED ON DOBLE OXIDATION STABILITY 750 p.s.i.g. 1.0 lb., a1. Bennett-Clark clay 300 F.

Hydrofining Temp 575 F. 475 F.

Feed, v./v.hr l. 0 2. 0 3.0 1. 0 2.0 Hz, S.c.f./b l 856 450 617 020 467 Samnln 1 2 3 4 5 Hrs. to 0.2 N .N 72 120 144+ 240 240 Hrs. to Sludge 72 72 72 48 48 Hits. to 15 IFT 72 120+ 144+ 240+ 240+ Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. An improved transformer oil having, when tested in the absence of inhibitors in the Doble oxidation test for electrical insulating oils, an interfacial tension of at least 15 dynes per centimeter, a neutralization number less than 0.2, and less than a trace of sludge after 48 hours, consisting essentially of a blend of 50-80 volume percent of a hydrofined oil boiling in the range of 460 to 775 F., having an API gravity in the range of 27 to 30, aviscosity at F. in the range of about 55 to 60 SSU and 50-20 volume percent of an acid-treated oil boiling in the range of 460 to 775 F. having an API gravity in the range of 27 to 30, a viscosity at 100 F. in the range of 55 to 60 SSU; said hydrofined oil being produced by contacting a distillate boiling in the range of 450 to 900 F. from a naphthenic crude with a hydrofining catalyst at a temperaturein the range of 550 to 650 F. and a feed rate in the range of 1 to 3 v./v./hr. in the presence of about 500 to 900 s.c.f./bbl. of free hydrogen, followed by treating the oil so hydrofined with in the range of 0.6 to 1 lb./gal. of an absorbent clay at a temperature in the range of 250 to 300 F., and said acid-treated oil being produced by treating at a temperature in the range of 85 to F. a distillate boiling in the range of 450 to 900 F. from a naphthenic crude with 0.5 to 1.0 lb./gal. of sulfuric acid having a concentration in the range of 96-105% and recovering the acid treated oil in yields in the range of 97 to 98 volume percent and further treating it by neutralization, steaming and clay percolation within the range of 0.6 to 1.0 lb./gal. of an absorbent clay at a temperature in the range of 80 to 105 F.

2. An'improved blended transformer oil consisting essentially of a blend of 50-80 volume percent of a hydrofined oil made at a temperature in the range of SSU-650 F. and boiling in the range of 460 to 775 F., and 50-20 apogee? volume percent of an acid-treated oil made by contact with 0.5 to 1.0 lb./ gal. of sulfuric acid having a concentration in the range of 96-105% and boiling in the range of 460 to 775 F. said hydrofined oil being prepared by contacting a distillate from a naphthenic crude with a hydrofining catalyst in the presence of hydrogen followed by treating the distillate oil so hydrofined with from 0.6 to 1.0 1b./gal. of an absorbent clay, and said acid-treated oil being produced by treating a distillate from a naphthenic crude with sulfuric acid recovering the distillate oil so treated with acid, neutralizing said oil so treated with acid, and treating the oil so neutralized with from 0.6 to 1.0 lb./ gal. of an absorbent clay.

3. A transformer oil in accordance with claim 1 wherein said hydrofined oil is produced from a distillate boiling 15 2,734 01 in the range of 460 to 775 F.

4. A transformer oil in accordance with claim 1 wherein said acid-treated oil is produced from a distillate boiling in the range of 460 to 775 F.

5. A transformer oil in accordance with claim 1 wherein said hydrofined oil and said acid-treated oil each have an API gravity in the range of 27 to 28.

6. A transformer oil consisting of a major amount of a blend in accordance with claim 1 and a minor and oxidation inhibiting amount of 2,6-di-tertiary butyl 4- methyl-phenol.

References Cited in the file of this patent UNITED STATES PATENTS 1,856,700 Ford May 3, 1932 2,472,217 Langan June 7, 1949 Miller Feb. 7, 1956 2,763,358 Linn et a1 Sept. 18, 1956 2,865,849 Van Loon et a1 Dec. 23, 1958 

1. AN IMPROVED TRANSFORMER OIL HAVING, WHEN TESTED IN THE ABSENCE OF INHIBITORS IN THE DOBLE OXIDATION TEST FOR ELECTRICAL INSULATING OILS, AN INTERFACIAL TENSION OF AT LEAST 15 DYNES PER CENTIMETER, A NEUTRALIZATION NUMBER LESS THAN 0.2, AND LESS THAN A TRACE OF SLUDGE AFTER 48 HOURS, CONSISTING ESSENTIALLY OF A BLEND OF 50-80 VOLUME PERCENT OF A HYDROFINED OIL BOILING IN THE RANGE OF 460* TO 775*F., HAVING AN API GRAVITY IN THE RANGE OF 27* TO 30*, A VISCOSITY AT 100*F. IN THE RANGE OF ABOUT 55 TO 60 SSU AND 50-20 VOLUME PERCENT OF AN ACID-TREATED OIL BOILING IN THE RANGE OF 460* TO 775*F. HAVING AN API GRAVITY IN THE RANGE OF 27* TO 30*, A VISCOSITY AT 100*F. IN THE RANGE OF 55 TO 60 SSU; SAID HYDROFINED OIL BEING PRODUCED BY CONTACTING A DISTILLATE BOILING IN THE RANGE OF 450* TO 900*F. FROM A NAPHTHENIC CRUDE WITH A HYDROFINING CATALYST AT A TEMPERATURE IN THE RANGE OF 550* TO 650*F. AND A FEED RATE IN THE RANGE OF 1 TO 3 V./V./HR. IN THE PRESENCE OF ABOUT 500 TO 900 S.C.F./BBL. OF FREE HYDROGEN FOLLOWED BY TREATING THE OIL SO HYDROFINED WITH IN THE RANGE OF 0.6 TO 1 LB./GAL. OF AN ABSORBENT CLAY AT A TEMPERATURE IN THE RANGE OF 250* TO 300*F., AND SAID ACID-TREATED OIL BEING PRODUCED BY TREATING AT A TEMPERATURE IN THE RANGE OF 85 TO 105*F. A DISTILLATE BOILING IN THE RANGE OF 450* TO 900*F. FROM A NAPHTHENIC CRUDE WITH 0.5 TO 1.0 LB./GAL. OF SULFURIC ACID HAVING A CONCENTRATION IN THE RANGE OF 96-105% AND RECOVERING THE ACID TREATED OIL IN YIELDS IN THE RANGE OF 97 TO 98 VOLUME PERCENT AND FURTHER TREATING IT BY NEUTRALIZATION, STEAMING AND CLAY PERCOLATION WITHIN THE RANGE OF 0.6 TO 1.0 LB./GAL. OF AN ABSORBENT CLAY AT A TEMPERATURE IN THE RANGE OF 80* TO 105*F. 